1. Field of the Invention
The present invention relates to a device for driving various accessories such as an alternator, a cooling water pump or the like, utilizing power of an engine of an automobile or the like.
2. Description of the Prior Art
In an engine of an automobile or the like, accessories such as an alternator, a cooling water pump, an air-conditioning compressor, an oil pump for hydraulic servo steering or the like are belt-driven by a crank pulley intalled at an end of a crank shaft. Since the accessory drive is accompanied with large power loss during the high speed running of the engine, in order to avoid it, various methods have been proposed that gear shifting of a crank pulley is performed with respect to the engine rotational speed and the running speed of the accessory is limited.
For example, Japanese patent application laid-open No. 200838/1983 discloses technology that a reduction drive system comprising a planetary reduction gear and a one-directional clutch, and a direct-coupled drive system comprising a lock-up clutch composed of a hydraulic piston are constituted between a crank shaft and a crank pulley of an engine, thereby the rotational speed of the crank pulley is selectively changed at two stages with respect to the engine rotational speed. In the prior art, however, since rapid speed variation is produced at the speed changing state, variation of the driving force of the accessory applies a variation shock to the vehicle driving force of the engine, thereby the running stability of the vehicle is deteriorated resulting in unpleasantness to the driver. Moreover, there are problems in durability of the planetary reduction gear, potentially resulting in noise. Consequently, this method is not practicable.
On the other hand, for example, Japanese utility model application laid-open No. 86434/1983 discloses technology utilizing a variable pitch pulley to vary effective pitch diameter, wherein a driving pulley of variable pitch is installed on a crank shaft, and a driven pulley also with variable pitch follows the driving pulley and integrally connects an accessory drive pulley. A movable sheave of the driven pulley is controlled by a hydraulic cylinder so as to control the accessory drive speed.
In this example of the prior art, the high hydraulic source is required to control the movable sheave of the drive pulley, and structure of the hydraulic actuator is considerably complicated. Further a comparatively wide installation space projecting in the crank axial direction of the engine is required. Consequently, this method is not suitable for a front wheel drive car with the engine laterally installed which is commonly used, because there is insufficient space for installation.